There are many transformer arrangements known in the prior art. Most of them include two or more coils where each coil includes one or more windings. Depending on the particular application, there are different kinds of windings such as for example wire windings, metal sheet windings, traces on a printed circuit board (PCB) and the like.
Most transformers which include a wire winding also include a bobbin, coil form or sleeve on which this wire winding is wound.
Document WO 2004/032158 (Delta Energy Systems) shows such a transformer. This transformer includes a coil form that is made of plastic and has a hole for insertion of a core. A first winding is formed by one or more separating plates that divide the outer surface of the coil form into two or more winding windows and a second winding is formed by a wire that is wound within one of the winding windows on the outer surface of the coil form. However, due to the coil form, the winding window utilization is low and there is a high thermal resistance between the core and the windings.
Document 2002/159214 A1 shows another transformer with a primary coil, a secondary coil and a magnetic core. The primary coil is a flat coil wound from a triple insulated wire and the secondary coil is formed by a trace on a PCB. While this transformer does not include a bobbin or the like but it includes a PCB which has to be produced in a separate step which makes it complicated and therefore expensive. Furthermore, this transformer is not suited for high power applications because neither the wire winding nor the PCB winding are suited for carrying a high current.